The present invention relates to guardrails of the type that are placed alongside a roadway to redirect a moving vehicle that has left the roadway.
Modern guardrails are relied on for two separate functions that are to some extent in tension with one another. First, the guardrail preferably has adequate tensional strength in the longitudinal direction that a vehicle striking an intermediate portion of the guardrail at an oblique angle will be prevented from passing through the guardrail and redirected along the length of the guardrail. This function requires considerable tensional strength.
Second, the guardrail preferably slows a vehicle that strikes the end of the guardrail at a suitable rate such that excessive decelerations are not applied to the vehicle and the guardrail does not impale the vehicle.
Various prior-art approaches have been suggested for accommodating these two separate functions of guardrail design. See for example, Sicking U.S. Pat. Nos. 5,547,309 and 5,407,298, Mak U.S. Pat. 5,503,495, and U.S. patent application Ser. No. 08/990,468 (U.S. Pat. No. 5,967,497), filed Dec. 15, 1997, assigned to the assignee of the present invention.
The present invention is directed to improvements in guardrails that further reduce any tendency of the guardrail to impale an impacting vehicle while maintaining a desired level of longitudinal tensional strength.